Counter-current automatic cleaning filter

ABSTRACT

The filter has a filtering chamber in which a number of hollow filtering elements are arranged on a circle about the axis of the filter. The chamber has a liquid inlet and a liquid outlet and the hollow filtering elements communicate in parallel with the inlet and outlet. A hollow arm defining a passageway is rotatable about the axis of the filter and the passageway is capable of putting all the inlets of the filtering elements successively in communication with an impurities discharging chamber in which prevails a pressure lower than the pressure of the filtered liquid. The arm is connected to rotate with the driven member of a unidirectional step-by-step drive mechanism. The arm is also connected to rotate with the driven member of a second unidirectional step-by-step drive mechanism in the same direction as with the first drive mechanism.

The present invention relates to devices for purifying or cleaningliquids such as hydrocarbons and more particularly concerns acounter-current purifying filter comprising a number of filteringelements which may be automatically cleaned by temporarily reversing theflow in each filtering element in accordance with a given sequence.

Filters of this type have been disclosed in German Patent PublicationsN° DAS 1,761,827 and DOS 2,021,918 and in particular in French Patent N°1,437,838, U.S. Pat. No. 3,380,591. In this latter prior publication,the filtering elements are constructed in the form of verticallydisposed columns arranged on a circle around the axis of the filter.Each element is put successively in communication with a rotary armforming a pipe which permits reversing the current of the liquid in theelement concerned for unclogging this element, a complete rotation ofthe arm having for effect to clean the whole of the filter.

The arm is rotated by a motor which advances the arm in a step-by-stepmanner so as to put it successively in coincidence with each filteringelement, this motor being supplied with the liquid to be cleaned.

In another filter of this known type, according to the First Addition tothe aforementioned French Patent, filed on the June 11 1965 under theP.V. 138,630, the step-by-step rotary arm advancing mechanism isdisposed outside the filter and comprises an electromagnet whichactuates at regular intervals a pawl which cooperates with a ratchetwheel connected to rotate with the shaft of the arm.

In these two types of filter, the unclogging obviously ceases when thestep-by-step drive mechanism breaks down, which does not however preventthe filter from operating normally until these filtering elements havebeen obturated by impurities extracted from the liquid to be cleaned.

But when the filtering elements are finally clogged up, the filterbecomes useless and must therefore be disconnected from the circuit inwhich it is mounted.

An object of the invention is to provide an automatic counter-currentcleaning filter wherein the unclogging may be carried out even when themotor driving the rotary arm breaks down or is blocked.

According to the invention, there is provided an automaticcounter-current cleaning filter comprising a number of filteringelements arranged on a circle defining an axis of the filter in afiltering chamber provided with a liquid inlet and outlet to which theelements are connected in parallel, and a hollow arm constituting a pipeand mounted to rotate about said axis and capable of successivelyconnecting all the inlets of said elements to an impurity dischargingchamber in which prevails a pressure lower than the pressure of thefiltered liquid, said arm being connected to be rotated by the drivenelement of the unidirectional step-by-step drive mechanism, wherein saidarm is also connected to rotate with the driven element of a secondunidirectional step-by-step drive mechanism in the same direction as thefirst step-by-step drive mechanism.

Owing to these features, the unidirectional step-by-step drivemechanisms may replace each other mutually even if one is blocked forsome reason, so that the unclogging of the filter can always be ensured.

According to another feature of the invention, the second step-by-stepdrive mechanism is controlled manually. Thus, it becomes possible, byputting out of action the first mechanism, to modulate the decloggingtime of a particular element among the filtering elements, by stoppingthe arm for a longer period of time on this element than would normallybe necessary in the course of the automatic procedure, for example if itis known that the amount of impurities retained by this element isparticularly large.

In the filters of the prior art mentioned hereinbefore, the automaticunclogging device is designed for each dimension of the filter or, inother words, for the number of filtering elements disposed about theaxis of the filter. This is due to the fact that the step or pitch ofthe step-by-step movement of rotation of the arm varies in accordancewith the angular spacing between the filtering elements.

Consequently, there must be provided for a given range of filters asmany unclogging devices as there are filters in this range.

According to another feature of the invention concerned moreparticularly with the avoidance of this drawback, the angular step orpitch of progression of the rotary arm for an angular spacing betweenthe filtering elements equivalent to a whole number of degrees is equalto a number which is prime to 360°.

Preferably, the value of this angular step corresponds to 7° at whichvalue the rotary arm is in exact coincidence with the inlet of eachfiltering element once in the course of a cycle of 7 rotations of therotary arm. Consequently, there is very satisfactory unclogging of allthe filtering elements of a filter irrespective of the number ofelements and the spacing therebetween.

Further features of the invention will be apparent from the ensuingdescription with reference to the accompanying drawings which are givensolely by way of example and in which:

FIG. 1 is an axial sectional view of a filter according to theinvention;

FIG. 2 is a sectional view, to an enlarged scale, of a first and asecond unidirectional step-by-step drive mechanism for the rotary shaftof the filter shown in FIG. 1;

FIG. 3 is a perspective view of a wheel employed in the mechanism shownin FIG. 2;

FIG. 4 is a diagrammatic view of the gears employed in the filteraccording to the invention, and

FIGS. 5 and 6 are diagrammatic perspective views showing how the step ofprogression through 7° of the rotary arm of the filter is achieved.

In the embodiment shown in FIGS. 1 to 4, the filter according to theinvention comprises a filter housing 1 of cylindrical shape divided intotwo compartments 2 and 3 by a radial partition wall 4, the uppercompartment 2 being defined by an inner cylindrical wall 5 which impartsthereto an annular shape. This inner wall 5 has a radial flange 6 boltedto the housing 1.

The latter has an inlet aperture 7 for the liquid to be filtered and anoutlet aperture 8 for the filtered liquid. The intermediate partitionwall 4 is provided with a series of screwthreaded openings 9 arranged ona circle around the axis X--X of the filter. Screwed in these openings,which constitute inlets, are the bases of as many filtering elements 10which are in the form of columns extending vertically upwardly from thepartition wall 4. It will be understood that the filtering elements maybe fixed in some other way in the filter. For example, in a modification(not shown) they may be each fitted into a cylindrical bore and made tobear against a flat joint element by a spring exerting a pressure on theopposite end of the corresponding filtering element.

The compartments 2 and 3 communicate with each other by way of theopenings 9 and the filtering elements. Note that the filtering elementsmay be constructed in any suitable way, their shape having no effect onthe performance of the filter of the invention, provided they can eachbe connected to an opening 9 of the partition wall 4.

Disposed at the centre of the bottom of the housing 1, is a supportplate 11 which constitutes a bearing for a driving shaft 12 having anaxis X--X and on which a rotary arm 13 is keyed. A passageway 14 whichhas substantially the shape of a Z turned through 90° is formed in thearm 13. This passageway communicates by way of the support plate 11 witha decanting chamber 15 connected to a discharge (not shown) which is atatmospheric pressure.

The passageway 14 may communicate selectively with each of the inletopenings 9 of the wall 4 in the course of the rotation of the arm 13.This rotation is brought about by a drive device which is shown in moredetail in FIGS. 2 and 3. This drive device 16 is disposed in the centralcylindrical space defined by the annular compartment 2 and is thereforeaccessible with no need to open the part of the filter in which thefluid flows. Moreover, this drive device is so designed that it isuniversal for a whole range of filters of this type irrespective of thesize, the number of filtering elements and the angular spacingtherebetween.

In the illustrated embodiment, the power supply is a hydraulic motor 17whose output shaft 18 is subjected to a continuous to-and-fro movementalong the axis thereof. The shaft 18 constitutes the input member of afirst unidirectional step-by-step drive mechanism 19 which comprises afirst ratchet wheel 20^(a) which is keyed on the shaft 18 and coaxialwith the latter. A coil spring 22 causes the wheel 20^(a) to engage,through dissymmetrical teeth 21, a second ratchet wheel 20^(b) (FIG. 3)provided with two helical ramps 23 projecting from the peripheralsurface thereof and in diametral relationship to each other.

The helical ribs or ramps 23 are engaged with complementary helicalgrooves 24 in the inner wall of a blind aperture 25 of a spindle 26which is rotatably mounted in the partition wall 4 of the housing 1, itsaxis Y--Y being parallel to the axis X--X of the filter. The spindle 26constitutes the driven member of the first step-by-step drive mechanism19 and is maintained by an extension 27 of the hydraulic motor 17through a needle rolling bearing 28 and a bearing surface 29 formed onthe spindle.

A gear pinion 30 is keyed on the spindle 26 and engages a gear wheel 31which is connected to the rotary arm 13 through the shaft 12 so as torotate with this arm. The gear wheel 31 is engaged with an intermediategear pinion 32 which is mounted on a pin 33 engaged in the partitionwall 4. The pinion 32 is engaged with a gear pinion 34 of the drivenmember 35 of a second unidirectional step-by-step drive mechanism 36.This driven member 35 is in the form of a spindle on which there aremachined the gear pinion 34 and a ratchet wheel 37^(a) which cooperateswith a complementary ratchet wheel 37^(b) through sets of dissymmetricalteeth 38. The wheel 37^(b) is keyed on an actuating rod 38 which extendsthrough the filter and out of the top of the latter and can receive anautomatically-return lever 39 which moves between two stops 40 having acertain angular spacing therebetween (for example 20°) relative to theaxis of the rod 38. The ratchet wheel 37^(b) is held in contact with thewheel 37^(a) by a coil spring 41 which bears against a shoulder 42 onthe rod 38.

The angular step of advance of the arm 13 is so chosen that the samedrive device 16 just described can be employed irrespective of thenumber of filtering elements 10 or the spacing therebetween. For anangular spacing between the filtering elements equal to a whole numberof degrees, the angular step is chosen to be equal to the number whichis prime to 360°, this number being preferably equal to 7°. Thus thedrive device 16 is capable of placing the arm in all the angularpositions corresponding to a whole number of degrees.

FIGS. 5 and 6 illustrate an embodiment in which the pair of ratchetwheels 20^(a) and 20^(b) effect a step of 20° for each to-and-fromovement of the shaft 18. Under these conditions, the set of teeth 21comprises therefore eighteen teeth. If twenty-one teeth are chosen forthe gear pinion 30 and sixty teeth for the gear wheel 31 (ratio 20/7),the arm 13 will move through a step of 7° for each movement of the shaft18.

The following table can thus be drawn up:

    ______________________________________                                        Rotation of the arm                                                                           Positions passed through                                      ______________________________________                                        1               0,       7,     14,  21   . . .                               2               4,      11,     18,  25   . . .                               3               1,       8,     15,  22   . . .                               4               5,      12,     19,  26   . . .                               5               2,       9,     16,  23   . . .                               6               6,      13,     20,  27   . . .                               7               3,      10,     17,  24   . . .                               8               0,       7,     14,  21   . . .                               ______________________________________                                    

Of course, it is possible to position the rotary arm with a precision of1° by choosing for the step a value of for example 11° or 13°. However,the advantage of employing an angle of 7° resides in the fact that, inthe course of a given rotation of the arm 13, a larger number offiltering elements is nearer to the position of complete coincidencewith the inlets of the elements.

If the angular spacing between the axes of the filtering elements isdifferent from a whole number of degrees, for example 0.5°, note thatthe linear spacing between these axes remains small, even if the radiusof the circle on which the elements are arranged is already relativelylarge. For example, in respect of a radius of 250 mm, 1° corresponds toan arc whose chord is about 4.3 mm, 0.5° corresponding to a chord of2.15 mm. Such a deviation from coincidence between the aperture of thearm 13 and the inlet of each filtering element is relatively small andwill permit a satisfactory unclogging of the element since a largecounter-current can be nevertheless created. Also, even if the angularspacing between the filtering elements corresponds to an angle whosevalue is not a whole number of degrees the unclogging can be achieved.

It can be seen from the foregoing description that the arm can berotated indifferently by the motor 17 or the manual control owing to thefact that the unidirectional drive mechanisms 19 and 36 are oriented inthe same direction. Thus, when the motor 17 operates, the ratchet wheels37^(a) and 37^(b) effect a relative movement of rotation in thedirection of the escape or disengagement of the teeth 38. Inversely, ifthe motor 17 does not operate or is blocked, the arm can be driven inrotation by movements of 20° of the automatically-returned control lever39, the extent of this movement being limited to this value by the stops40 while the ratchet wheels 20^(a), 20^(b) effect a relative movement inthe direction of the escape or disengagement of their teeth 21.

According to a modification, a motor may be provided, at the input endof the second step-by-step drive mechanism 36 instead of the manualactuating mechanism, to replace the motor 17 in the event of breakdown.

Thus it can be seen that the hydraulic motor 17 may be blocked or evendisassembled without this preventing the filter from operating. It isthen sufficient to unclog the filter either manually or by means of amotor coupled to the second drive mechanism. If the control is manual,the unclogging has no need to be continuous but it can be carried outtwice a day, for example if it concerns a filter for hydrocarbons,without hindering the good operation of the filter. On the other hand,if the control is automatic, the motor 17 preferably operatespermanently.

Having now described my invention what I claim as new and desire tosecure by Letters Patent is:
 1. An automatic counter-current cleaningfilter comprising a housing having an axis, means defining a filteringchamber in said housing, a number of hollow filtering elements havinginlets and outlets and arranged on a circle centered on said axis in thefiltering chamber, the filtering chamber having a liquid inlet and aliquid outlet with which liquid inlet and liquid outlet the interiors ofthe filtering elements communicate in parallel, an impurity dischargingchamber in which prevails a pressure lower than the pressure of thefiltered liquid, and a hollow arm defining a passageway and mounted torotate about said axis and capable of successively connecting as itrotates about said axis all the inlets of said elements to the impuritydischarging chamber by way of said passageway, a first unidirectionalstep-by-step drive mechanism having a driven member, a secondunidirectional step-by-step drive mechanism having a driven member, andmeans connecting the arm to be driven by the driven member of the firstdrive mechanism and means connecting the arm to be driven by the drivenmember of the second drive mechanism in the same direction as it isdriven by the drive member of the first step-by-step drive mechanism. 2.A filter as claimed in claim 1, comprising means for manuallycontrolling said second unidirectional step-by-step drive mechanism. 3.A filter as claimed in claim 2, wherein said second unidirectionalstep-by-step drive mechanism comprises a driving member and an actuatingrod coupled with the driving member, the filter further comprises acontrol lever located outside the filter and rotatable between a firstposition and a second position, and means for automatically returningthe control lever to said first position, the acuating rod beingconnected to so as to rotate with said lever.
 4. A filter as claimed inclaim 3, comprising a motor having an output member which is capable ofundergoing a continuous to-and-fro movement, the first step-by-stepdrive mechanism having a driving member and means coupling the drivingmember of the first drive mechanism to the motor.